Disc drive systems have been used in computers and other electronic devices for many years for storage of digital information. Information is recorded on concentric memory tracks of a magnetic disc medium, the actual information being stored in the form of magnetic transitions within the medium. The discs themselves are rotatably mounted on a shaft or “spindle”, the information being accessed by means of transducers located on a pivoting arm, which moves radially over the surface of the disc. The read/write heads or transducers must be accurately aligned with the storage tracks on the disc to ensure proper reading and writing of information; thus the discs must be rotationally stable.
Electric spindle motors are used to rotate the discs in disc drive systems. Such spindle motors may have either a fixed shaft and a rotating sleeve or a fixed sleeve and a rotating shaft. Depending on the type of spindle motor, a rotor hub is affixed to either the rotating shaft or to the rotating sleeve. The disc is then mounted on the rotor hub.
The spindle motor's shaft and sleeve must be rotatably mounted to each other so as to allow relative rotation between the shaft and sleeve, but so as to minimize lateral and axial motion as well as tilting motion. Fluid dynamic bearings are the preferred method of providing such mounting, although conventional ball bearings are sometimes used.
In fluid dynamic bearings, a thin film of a lubricating fluid—either gas or liquid—functions as the bearing surface between the sleeve and the shaft. Pressure generating grooves on either the sleeve or the shaft generate pressure gradients in the fluid that prevent the sleeve and the shaft from contacting each other during motor operation. The bearing properties such as stiffness and energy consumption as well as the cost of the bearing are dependant upon many factors such as the bearing dimensions and shape, the positioning of the grooves, and the size of the gaps between the sleeve and shaft.
The requirements for a specific spindle motor vary depending on the application in which the spindle motor will be used. Since hard disc drives are used for a large variety of applications, there is a need for a variety of types of spindle motors to meet the specific requirements of the various applications. Accordingly, there is a need to efficiently manufacture a variety of types of spindle motors, where each type of spindle motor is closely matched to the specific requirements of the applications for which it will be used.
The manufacture of fluid dynamic bearings is a labor intensive process that requires numerous steps including machining the components, etching the grooves, applying oil repellent film, assembling the components, and adding the lubricant. In the prior art, as shown in FIG. 1, the bearing and the spindle motor are manufactured together as a single unit and the bearing is an integral part of the spindle motor.